5.10.1 Specific Compiler Characteristics

Some compilers exhibit different behaviors.

Static/Dynamic Expressions

Autoconf relies on a trick to extract one bit of information from the C
compiler: using negative array sizes. For instance the following
excerpt of a C source demonstrates how to test whether ‘int’ objects are 4
bytes wide:

static int test_array[sizeof (int) == 4 ? 1 : -1];

To our knowledge, there is a single compiler that does not support this
trick: the HP C compilers (the real ones, not only the
“bundled”) on HP-UX 11.00.
They incorrectly reject the above program with the diagnostic
“Variable-length arrays cannot have static storage.”
This bug comes from HP compilers' mishandling of sizeof (int),
not from the ? 1 : -1, and
Autoconf works around this problem by casting sizeof (int) to
long int before comparing it.